We propose a study using both existing data and a new longitudinal survey of approximately 4,000 individuals to study the relationships among migration, urbanization, and health. Our project is designed to help resolve confusion in the migration-urbanization-health nexus, with direct policy implications for South Africa and both substantive and methodological lessons for a broad array of scientific concerns in Low and Middle Income Countries (LMICs). A better understanding of the way in which these redistributive forces operate on health (and its complex interplay with economic development) can help inform global health policy by (1) improving our understanding of how migration and urbanization impact population health, so as to better understand the trade-off between the salutary increases in socioeconomic circumstances associated with urbanization (the increasing share of a population residing in towns and cities, as distinct from the urban growth rate) and the health risks that accompany that shift; (2) improving our understanding of population redistribution, so as to be better equipped to incorporate spatial demography into companion health investigations; (3) identifying circumstances where population mobility itself may compromise the treatment cascade - compromising the continuity necessary to deliver suitable health care for chronic conditions; and (4) building scientific capacity in the region. We plan to conduct a new five-year observational study aimed at shedding light on issues of how mobile individuals acquire and manage chronic diseases and access long-term care, combining insights from a new longitudinal cohort study of 4,000 migrants and stayers and more than twenty years of extant data for a population of now more than 100,000 in demographic surveillance. Our study site is a district in rural northeast South Africa and the locations to whih migrants from that origin move. We carry out this study to better understand, at the individual level, how a contemporary, complex pattern of migration and urbanization helps drive the health transition in low and middle income countries. Our innovative approach gathers new data on an array of socioeconomic variables and life history items, health conditions, behaviors, and selected biomarkers. We study several intertwined demographic and health dynamics. We examine the determinants of risk factors for key health outcomes. We measure health care access and treatment, and test whether barriers to care are posed by migration. We also investigate migration dynamics directly so as to better to understand the determinants of population redistribution and the paths of migrant adjustment in destinations.